The present invention relates to an analog-to-digital (A/D) conversion circuit with a carrier frequency removing feature. More particularly, the present invention is concerned with an A/D conversion circuit with a carrier frequency removing feature capable of fully removing a carrier-frequency component despite a compact low-cost configuration.
Diagnostic ultrasound systems have been known in the past, wherein a baseband signal is sampled from an ultrasonic signal received in a continuous-wave Doppler mode, a high-pass filter is used to remove a carrier-frequency component from the ultrasonic signal that has the baseband signal sampled therefrom, and the signal having the carrier-frequency component removed therefrom is converted into digital data by an A/D converter (refer to, for example, Patent Document 1).
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-57525
In the conventional diagnostic ultrasound system, a signal having a carrier-frequency component removed therefrom is converted into digital data by an A/D converter. An A/D converter designed to treat, for example, 12 bits can offer a dynamic range that is wide enough to handle a signal component having undergone a Doppler shift. A compact low-cost configuration ensues.
However, a method of removing a carrier-frequency component using a high-band filter cannot fully remove the carrier-frequency component.